These studies are directed toward understanding the molecular basis of cellular differentiation. Friend erythroleukemia (FL) cells provide an excellent model system for this type of investigation since they undergo erythrodifferentiation to a hemoglobin-producing stage both in tissue culture and in vivo. Erythrodifferentiation is stimulated in these cells by dimethyl sulfoxide (DMSO) and many other inducers. The levels of erythroid-characteristic components such as hemoglobin and globin mRNA as well as several erythroid-compatible cellular components are increased during this process. It has been shown in our laboratory and that of others that differentiation in this system is accompanied by single-stranded breaks in DNA. Some inducers of this system are lysosome-activators in other systems. Lysosome-stabilizing agents inhibit induction in FL cells (unpublished data). Therefore it is proposed that the molecular processes controlling FL cell differentiation include the following steps: The inducer enters the cell, affects lysosomal membranes and a DNAase is triggered to leave the lysosome. The enzyme travels to the nucleus and reaches the chromatin where it directs specific cleavages in DNA. These DNA breaks are hypothesized to initiate transcription of differentiated products such as the three types of globin found in FL cells. Therefore in this investigation studies concerning DNA breakage and lysosome activation or stabilization are planned. DNA breakage will be studied by alkaline sucrose gradient analysis and by analysis of folded genomes isolated on neutral sucrose gradients. Characterization of the DNAase responsible for these breaks in DNA and changes in folded genomes will be undertaken. The relationship of lysosome integrity to differentiation will be studied. Other systems that differentiate in response to DMSO (granulocytes and neuroblastoma cells) will be tested for DNA breakage. The state of DNA in FL cell mutants resistant to DMSO or other inducers also will be studied.